After a decade of database consulting, slow queries are almost never mysterious. Ninety percent trace to three causes. One: the query is fine but the index is missing, so the database reads the whole table to find one row. Two: the query is secretly a loop. It looks like one query but an ORM turned it into a thousand hidden queries. Three: your statistics are stale, so the optimizer picks yesterday's plan for today's data. Before you shard anything or add a cache layer, check these three. Add the index, kill the loop, refresh the stats. I have solved more production incidents with those three moves than with every exotic optimization combined.